1. Field of the Invention
The present invention relates to a shadow mask in a cathode ray tube, and more particularly, to a shadow mask in a cathode ray tube, which has a structure that can prevent formation of wrinkles and improve deterioration of purity characteristics caused by the formation of wrinkles.
2. Background of the Related Art
Referring to FIG. 1, a related art color cathode ray tube is provided with a front glass called as a panel 10, a funnel 12, a bulb form of rear glass, a fluorescent surface 11 having a coat of luminous fluorescent material on an inside surface of the panel, an electron gun sealed in a neck of the funnel for emitting electron beams to make the fluorescent surface luminous, a shadow mask 13 for selecting a color from the electron beams passed therethrough to make the fluorescent material luminous, and a frame 15 for supporting the shadow mask 13. A frame assembly of the frame 15 and the shadow mask 13 is fitted to the panel 10 by springs 16. Further, there is an inner shield 17 in rear of the frame assembly in the cathode ray tube which is at a high vacuum for shielding an influence of an external geomagnetism during operation of the cathode ray tube.
In the related art color cathode ray tube, upon application of an anodic voltage to the cathode ray tube, the electron beams are emitted from the electron gun, and hit onto the fluorescent surface 11 formed on the inside surface of the panel 10, which are deflected by a deflection yoke 14 in an up, down, left, or right direction before the electron beams reach to the fluorescent surface 11. The deflected electron beams are subjected to color selection as the electron beams pass through a plurality of slots in the shadow mask, land on the fluorescent material of the fluorescent surface, and make the fluorescent material luminous, to reproduce a picture.
The shadow mask is welded to a frame structure shown in FIG. 2A, which is shown in FIG. 2B as a top view and in FIG. 2C as a perspective view. One pair of main frames 15-1 and subframes 15-2 are welded together to form a rectangular frame, wherein the pair of the main frames 15-1 are welded on the pair of subframes which are arrange opposite to each other opposite to each other. The shadow mask 13 having a plurality of slots formed therein as shown in FIG. 2B is welded on such a frame structure. A frame assembly as shown in FIG. 2C is formed by welding the shadow mask 13 on top of the main frames under a state the subframes 15-2 are bent by a compressive load T applied to the main frames 15-1 and releasing the compressive load applied to the main frames, to exert a tensile force to the shadow mask 13. If an amount of elongation by the frames are not adequate, the pre-stressed shadow mask 13 assembled thus shows a serious howling caused by external vibration. Though howling in a central portion of the pre-stressed shadow mask 13 is not distinctive because an incident angle of the electron beams to the central portion is not great even if the shadow mask vibrates in an up or down direction by an external impact, the howling in a periphery and corners of the pre-stressed shadow mask 13 is distinctive because the incident angle of the electron beams to the periphery and corners of the shadow mask is great to move the electron beams heavily such that the electron beams can not land on the fluorescent material exactly, to deteriorate a color purity of the picture. Therefore, as shown in FIG. 3, the compressive load on the main frame 15-1 is made to vary with location of the main frame 15-1, and a thickness of the shadow mask 13 is set to be below 0.1 mm for an adequate elongation of the shadow mask by means of a little compressive load. However, as shown in FIGS. 4 and 5, the effective surface 13-1 having the slots formed therein and the non-effective surface 13-2 having no slots formed therein of the pre-stressed shadow mask 13 have different modulus of elasticity owing to difference of geometry of structure, that is, the modulus of elasticity of the effective surface 13-1 is smaller than the modulus of elasticity of the non-effective surface 13-2, to have a displacement xcex4 of the effective surface 13-1 greater than a displacement of the non-effective surface 13-2, to form wrinkles at left and right sides (xe2x80x9cAxe2x80x9d part) of the effective surface 13-1 as much as a difference of the displacements. The wrinkles at the sides (xe2x80x9cAxe2x80x9d part) of the effective surface 13 deforms the shadow mask 13, to change locations of the slots the electron beams pass therethrough, resulting in a poor color purity of the picture reproduced on the cathode ray tube.
Accordingly, the present invention is directed to a shadow mask in a cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a shadow mask in a cathode ray tube, which can prevent wrinkles from being formed at sides of an effective surface for enhancing a color purity of the picture.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the shadow mask in a cathode ray tube includes an effective surface, and a non-effective surface, wherein the effective surface includes elongated slots each extended in full length of the effective surface without bridges between slots in a vertical direction at left and right outermost sides of the shadow mask or outer side slots adjacent to the outermost side slots.
The elongated slot has a width expressed by the following inequality.
SWm less than SWgxe2x89xa6SWm+(+xcex4y)/3,
where, SWg denotes width of the elongated slot, SWm denotes a width of conventional slot, and +xcex4y denotes a vertical elongation of the shadow mask.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.